Method of impregnating carbonaceous bodies



' June 21 1949 LE ROY s. DUNHAM E1-AL 2,473,943-

' METHOD or' IMPREGNATING cARBoNAcx-:ous BODIES Filed April s, 194s 7 15 i1 5 *"9 -i- E .i L-l E Il v/fuf KOH :i m2212401. 7/ "Il: w 3

j h--3 t# 'f n "il, Y /5 l ,f 'X10' j cl' INVENTORS Leoz/ 5'. .Dunham BY Ez'rzar V Secezsez Y ATTe/VEY 5? fr?. i!" fr 4,/ n L Patented June 21, 1949 UNITED STATES PATET OFFICE METHOD OF IBIPREGNATING CARBONA- CEOUS BODIES Le Roy S. Dunham, East Orange, and Einar V. Steffensen, Belleville, N. J., assignors to Thomas A. Edison, Incorporated, West Orange, N. J., a corporation of New Jersey Application April 6, 1945, Serial No. 586,950

1 claim. 1

, ject of our invention to provide such an electrode having these improved characteristics.

Another object is to providev a new and improved process for producing such an improved electrode.

It is another object to provide an improved depolarizing electrode, or cathode, for primary cells having an improved space eflciency enabling the construction of smaller cells with higher service capacity.

It is another object to provide a novel construction cf primary cell wherein this improved electrode is advantageously employed.

Other objects and features of our invention will appear from the following description and the appended claim.

In the description of our invention reference is had to the accompanying drawings, of which:

Figure 1 is an elevational view, partly in vertical section, showing a preferred construction of primary cell incorporating our invention;

i Figure 2 is a view taken' substantially on the line 2-2 of Figure 1;

Figure 3 is a vertical sectional view taken on the line 3-3 of Figure 2, but omitting the spacers between the electrodes.

Figure 4 is a fractional perspective view of the electrode assembly of the present illustrative embodiment; and

Figure 5 is a fractional perspective view of a cathode assembly according to the present invention.

In the accompanying figures we show a preferred construction of a primary cell of a deferred action-high current according to our invention. This cell has a rectangular case I preferably molded of a suitable plastic such as polystyrene. Within the case is'an electrode assembly comprising a series of alternately-arranged anodes and cathodes 2 and 3 disposed vertically in spaced parallel relation to one another.. Successive pairs of the anodes consist of single sheets 4 of amaigamated zinc folded into a U shape. Within and between these sheets 4v are the successive cathodes 3. These cathodes consist oi plates 5 of porous carbon impregnated with mercurio oxide according to our invention as is hereinafter particularly described. Long thin plates of the impregnated carbon material, such as are preferably employed in the present variety of battery, are somewhat frangible and need therefore to have a supporting frame. This frame consists of top and bottom channel members E joined mechanically and electrically at the ends by wire members 'l and 8. The channel members are for example apertured at the ends to receive the wire members after the plates 5 are set therein, and

' the wire members are then secured to the channel members by soldering. The channel members and wire members may be made of steel, Monel, nickel plated base metal, and the like.

'IIhe catho'des and anodes are spacedfrom one another by surrounding bands or cords 9 of cotton or rubber, this being a preferred way of effecting the spacing because it provides the least obstruction between'adjacent electrodes and iin-' proves therefore the performance of the battery.

The sheets 4 areujoined to one another at the bottom by lzinc strips ID soldered thereto and one of the outer sheets has a lug I I turned over at the top to which is soldered a Wire Ila. This wirev serves as a means for making electrical connection to the anode group. One set of the Wire members 'I of the cathodes extend above the top channel membersl and are `soldered together,

as to a conducting strip I2; but one intermediate lof hollow terminals I4 and I5 which are sealed liquid-tight thereto. The Wires la and IIa are threaded through these terminals as the cover is mounted in place, and then the cover is sealed by plastic cement to the case and the terminals arev sealed and joined to the wires by soldering. The cover has a central iiller opening I6 which is closed liquid-tight prior to the introduction of electrolyte by a screw plug Il and gasket I8. The electrolyte to be added is a solution of caustic alkali. At the time of adding the electrolyte, the gasket I8 may be discarded vand the plug reinserted so as to provide a splash-'resistant closure which will let out the internal gases.

,There is some tendency `for a porous carbon body impregnated with a water-soluble sait to develop surface areas which will not wet easily by caustic alkali electrolyte, it being understood that wetting is essential to get the electrolyte in association .with the cathode so that the cell will operate. This tendency is believed to be due to an excess of the Water-soluble salt being formed on the surface of the carbon body, and may also `be caused by organic solvents which may be used in the sealing cement used on the case. We nd that this non-wetting difliculty may however be readily overcome by adding to the electrolyte a small percentage of alcohol, say 5%.

The present cell of our invention is distinguished by an unusually high efiiciency in respect of its service capacity per unit volume thereof. A feature of this cell which contributes particularly to this high emciency is in the use of carbon cathode bodiesthe plates 5-which are impregnated with unusually large amounts of mercuric oxide. As a rst requirement to obtain this high degree of impregnation, we employ a special carbonaceous material-which serves as a skeleton for the depolarizing or active material of the cathodehaving a markedly high degree of porosity and, by the same token, a relatively low apparent density. Preferably, we employ carbon bodies having a porosity between 50% and 60%- the term percentage porosity being employed to mean the ratio of volume of air space to total occupied space of the whole bodyand having a density between .9 and 1.2 g. per cu. cm. It is to be understood, however, that our invention contemplates the use, as well, of other porous conductive bodies such as of metal, which are madeV so as to have a like percentage porosity.

A carbon body having the physical characteristics above described has been produced in accordance with our invention by mixing four parts by weight of finely ground coke (preferably 100 mesh) with one part by weight of nely ground gilsonite and enough of a saturated solution of ammonium chloride to form a plastic mass, a satisfactory mix being obtained for instance by mixing these ingredients in a ratio of 80 g. of the coke with 20 g. of the gilsonite and 9 cu. cm. of ammonium chloride. This mix is then placed in a die under pressure of approximately 2 1/2 tons per sq. in., thereafter dried and thenfired in a furnace out of contact .with air at a temperature between 1600 F. and 1700cl F. The carbon bodies so formed are self-sustaining blocks of essentially pure retort carbon, or a substantial equivalent thereof, and have an apparent density of .97 and a porosity of between and 60%. By using coke of different iineness, the porosity may however be varied.

These carbon bodies are impregnated with mercuric oxide by an improved method according to our invention, which is as follows: A brine solution of mercuric chloride is made by mixing approximately 66.7% mercuric chloride (HgCh) with 24.7% water and 8.6% common salt (NaCl). The carbon body is saturated with this mercuric chloride solution, for instance, by immersing the body therein under a vacuum or while the solution is at a temperature of approximately 100 C. The body is then removed and dried at approximately 100 C. Thereafter, the body is immersed in a Vhot (typically C.) 20% solution of caustic alkali, preferably caustic soda, and let stand therein for approximately one to two hours. In this step caustic alkali reacts with the mercuric lchloride and precipitates mercuric oxide, leaving the oxide distributed throughout the pores of the carbon body. After this precipitation is completed, the carbon body is removed from the caustic soda solution, Washed with water and dried at approximately C. g

The above described series of steps completes one cycle in the process of impregnating the carbon body with mercuric oxide. This cycle is repeated until the body is impregnated tothe desired degree, the number of cycles required depending primarily upon the thickness of the carbon body. For example, we nd ve cycles are generally suiiicient for a carbon body 11g" thick.

By-the above described impregnating process,

we are able in ve cycles to incorporatev as much g as 6 g. of mercuric oxide into a carbon body 2 square and s" thick. This is an impregnation of the order of 1.5 g. of mercuric oxide per cu. cm. of the carbon body, which is an impregnation equal approximately to .0137 faradic equivalents per cu. cm. Moreover, this process leaves no end products in the carbon body which have any re'- sultant harmful effects. While we may use other mercuric salts for this starting solution, say mercuric nitrate, this is not as desirable because if some of the nitrate were left as a residue it would have a destructive action on'the carbon body. Mercurio chloride has however no such destructive action.

The carbon material itself of the cathode serves as a skeleton or framework for carrying the depolarizing material and for conducting the current therefrom. Since the amount of active material which is incorporated into the porous cathode body determines the capacity of the cell, the service capacity per unit of overall volume of the cell is made very great. Also, this cathode does not cause appreciable expansion of the electrolyte or undue gassing during operation of the cell, which is very important in most battery applications. It is moreover an advantageous characteristic of this cathode that it functions reliably and efficiently at extremely low temperatures.

It will be apparent to those skilled in the art that the carbon body herein described may be im vare much inferior to those Whichare impregnated with mercuric oxide.

The following quantitative data is illustrative of the high performance which is attainable in primary cells by the use of our invention: The cell herein specifically described has live impregnated carbon plates each approximately g1g thick by 2" high by 4" long, and six associated zinc anode plates approximately .006 thick and dimensions in height and length like those of the carbon plates. This electrode assembly mounts readily into a container which-is 1%" thick by 21/2 high by 41/2 long. When the container is filled with a caustic alkali solution of suitable strength, preferably a 30% solution of potassium hydroxide, the cell will supply continuously for four hours 2 amp. of current at approximately 1.3 average volts, and will do so at temperatures 4 as low as 40 F. This is an unusually high service capacity per volume and weight of the cell.

The embodiment of our invention herein shown` and described is intended as being illustrative and not necessarily limitative of our invention as the same is subject to changes and modifications without departure from the scope of our invensaid body a bring;L solution of a mercurio saltecomposed approximately Vo1"66.'7% mercurio chloride, 24.7% water and 8.6% sodium chloride,^grying saidmbody, irrimerjsing said body in asoiutioi cistc'alkali havir'g` atempi of the order o`f60 CI so as to precipitate' mercuric oxide within said body throughout the pores thereof, and repeating said process until approximately 1.5

body per cu. cm. of volume thereof.

UNITED STATES PATENTS Number grams of mercurio oxide are deposited within said 15 2 178 969 LE ROY S. DUNHAM. EINAR V. STEFFENSEN.

.REFERENCES CITED Number Name Date Berliner Jan. 23, 1883 Haid Oct. 16, 1883 Molera et ai Jan. 8, 1884 Wilder Dec. 20, 1887 Schroeder Aug. 6, 1889 Schoenmehl Mar. .11, 1913 Saltzman Jan. 26, 1915 French et al Nov. 19, 1918 Runoff Sept. 20, 1921 Wilker Nov.'7, 1922 Wheat Aug. 30, 1932 Pautou Apr. 9, 1935 Ruben Nov. '7, 1939 FOREIGN PATENTS Country Date Great Britain 1886 OTHER REFERENCES Lowry, Inorganic Chemistry, MacMillan & Co. Ltd.. London, 1931, p. 907. 

